Thermodynamic Properties of Sodium n-Alkanecarboxylates in Water and in Water + Cyclodextrins Mixtures

Abstract

Densities and heat capacities of water−substrate, water−cyclodextrin, and water−substrate−cyclodextrin systems were determined at 298 K. The substrates studied are sodium n-alkanecarboxylates (C n COONa) (from sodium acetate to sodium decanoate) and the cyclodextrins are hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin, (HP-β-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and β-cyclodextrin (β-CD). The apparent molar volumes and heat capacities of C n COONa in water were calculated as functions of concentration. The standard partial molar properties agree with those obtained by using the additivity rule. HP-β-CD essentially does not affect the thermodynamic properties of C1COONa and C2COONa. Contrarily, the formation of the inclusion complex between cyclodextrin and substrate modifies the apparent molar properties. From the standard partial molar properties of the substrate in pure water and in water + HP-β-CD mixtures and literature values for the equilibrium constant for the inclusion complex formation, the standard partial molar properties of the complex ( ) were calculated. The increase of with the number of carbon atoms in the alkyl chain (n) is consistent with the solubilization of methylene groups in the hydrophobic cavity of the cyclodextrin and the expulsion of some water molecules from the cavity. To explain the dependence of on n, conformational effects are also invoked. Studies performed as functions of cyclodextrin concentration evidence that micellization occurs provided that all the cyclodextrin is almost complexed and that the dispersed surfactant concentration equals its critical micelle concentration in water. Data in HP-α-CD, HP-β-CD, HP-γ-CD, and β-CD indicate that the size cavity of the cyclodextrin strongly affects the thermodynamics of the inclusion complex formation while the nature of the hydrophilic shell of the cyclodextrin does not.

Volumes of aqueous block copolymers based on poly(propylene oxides) and poly(ethylene oxides) in a large temperature range: A quantitative description

“…The standard enthalpy [15,16,24,25] of micellization is usually evaluated from the cmc dependence on temperature [36] by assuming that the heat capacity of micellization is null. This is not a general rule since a negative change of the heat capacity is obtained for these copolymers [27,29,32,33,35] in agreement with the hydrophobic desolvation which accompanies the micelles formation [37][38][39]. Scarce are the investigations of the thermodynamic properties (enthalpy [17,18], density [18][19][20][21][22][23]26,27,30], compressibility [20,21,26], expansibility [30] and heat capacity [26,27,29]) obtained from direct measurements.…”

(Surfactant+polymer) interaction parameter studied by (liquid+liquid) equilibrium data of quaternary aqueous solution containing surfactant, polymer, and salt

“…Determination of (polymer + surfactant) interaction can be done by calorimetry and voltametry method [19][20][21][22][23], but in this work, we have used LLE of aqueous quaternary system containing surfactant, polymer, and salt for determination of (polymer + surfactant) interaction parameter. In the present work the FloryHuggins model has been used for correlation and prediction of the behavior of the quaternary aqueous systems.…”

Effect of β-Cyclodextrin on the Micellization of Cetyltrimethylammonium in Aqueous Solution at High Temperature

“…Other similar systems have been investigated by density and kinetics. [11][12][13] A deeper understanding of the effect of b-CD on the micellization of surfactants is important to aid in their utilizations, and so far this aspect has not yet been thoroughly investigated.…”